Apart from the exception cwa107 mentioned, I've seen no reason for anyone to install Adobe Reader when they already have Preview.
As for Flash, I'm hoping 2011 was just a really bad year for them security wise (seemed like they updated it every couple of weeks to fix critical bugs) and that they're back on track with it. You should download the latest Flash your machine will run (the Adobe Flash page will auto-determine this for you), but I would also suggest a flash blocker for your web browser (I don't hate ads, but I *do* hate auto-playing, animated, noisy or distracting ads, which is Flash's primary speciality).